Farmers in South Australia's mid-north say they can't believe their properties have been flooded only weeks after being burnt out by bushfires.

All of Russel Zwar's land was destroyed during the Bangor fire, which burnt for a month. Then on Friday, rain started to fall and didn't stop.

Mr Zwar says he was worried that after surviving the fire, all his topsoil would be washed away.

"I was in the town in Wirrabara when it first started falling heavily, and on my way home. I just saw a phenomenal amount of water coming off the paddocks, and some of it was more water than I've seen in a long time, if ever," he said.

"The closer we got to home, I was getting pretty worried as to what we were going to see when the water subsided, but luckily it seems to have escaped it fairly well, which is relieving."